1. Suppose that after x seconds, the area of PBQ is equal to 4 square centimeters.

PB=5-X

OB=2X

(5-X)*2X*( 1/2)=4

(X-4)*(X- 1)=0

X=4 or X= 1

Because 2X is less than or equal to 7 cm

So X= 1.

2. Let the length of PQ after x seconds be equal to 5cm.

PB=5-X

BQ=2X

PQ^2=PB^2+BQ^2

(5-X)^2+4X^2=25

X=2 or X=0.

If x is 0, PQ=AB, it does not exist, △PBQ.

So X=2.

Step 3: No.

If the area is equal to 7,

(5-X)*2X*( 1/2)=7

5X-X^2-7=0

(X-2.5)^2=-0.75

No answer

So it can't be equal to 7 square centimeters.